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The OHMA weld cylinder has several unique features that
distinguish it from both conventional pneumatic weld cylinders
and other types of air over oil intensifier cylinders.
Ratio
All OHMA weld cylinders are designed to produce a specific
force ratio. The ratio represents the factor by which air
pressure is internally multiplied to produce the weld force.
For example, a 22:1 ratio OHMA weld cylinder will produce
22 lb. of force for every 1 PSI introduced to the Intensifier
Port (EE3). In other words, sequencing 60 PSI of regulated
pressure to EE3 will result in the cylinder developing (60
PSI x 22) 1320 lb. of weld force.
Power Stroke and Advance Stroke
The power stroke represents the stroke the cylinder produces
during the high pressure portion of the sequence of operation.
The power stroke is limited to, and is a function of, the
cylinder's physical configuration. For example, a 32:1 ratio
cylinder with a 3" overall stroke and .20 power stroke operating
at 45 PSI will initially make contact with the work as if
it were an air cylinder. In this particular example, the
advance force would be equal to the cylinder bore area multiplied
by the air pressure (3.1416 x 45 PSI); this would equal
141 lb.. Upon initiation of the power stroke stage, the
force would be boosted by the ratio to 1440 lb.. (32 x 45
PSI). The maximum distance that the cylinder will travel
at this force will be .20". Although the power stroke may
appear to be short, a vast majority of spot welding applications
will require a stroke length well within this range.
It is important to note that the power stroke can be initiated
anywhere within the advance stroke range. This is defined
as the overall stroke minus the power stroke. In our example
the advance stroke range would be: 3" - .20" = 2.80". Effectively,
this means that the OHMA cylinder can develop the power
stroke anywhere from 0" to 2.80". Where the power stroke
is initiated within the advance stroke range will have no
effect on the ratio or the power stroke length. In order
to further illustrate this important concept please consider
the following example:
An OHMA weld cylinder with a 2" bore, 22:1 ratio, 5" stroke,
.26 power stroke operating at 50 PSI will:
have an initial advance force of 157 lb (3.1416 {area of
2" bore} x 50 PSI)
develop 1,100 lb of weld force (22 {ratio} x 50 PSI)
will have the ability to stroke for a distance of .26" at
the rated weld force
will be able to develop the power stroke anywhere from 0"
to 4.74" (5" - 0.26")
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